The invention concerns a method and a device for regulating the sliver in a card, that is a machine having a main cylinder provided with a clothing which cooperates with working elements (for example travelling flats) distributed around the circumference of the main cylinder. The cooperation of the main cylinder clothing with these operating elements generates a carding effect. A machine of this kind also comprises a material feed with, for example a licker-in and a feed roll, the rate of revolutions of the feed roll being controllable. The machine also comprises a so-called delivery section including a doffer which takes a fibre web from the main cylinder and transfers it to the machine outlet.
The invention relates to a method and a device for controlling a card during a so-called "transient" phase, that is during a period in which the delivery speed is being changed. Examples of such phases are the acceleration phase during running up to operating speed, the braking phase during stopping of the card and the corresponding acceleration phases (positive and negative) during can changing.
The conventional procedure during running up to speed and braking will subsequently be described in more detail with reference to the figures. This procedure serves as an example of a "transient" phase, the other transient phases proceeding correspondingly.
As is known, however, this procedure, which is still conventional, leads to an "unstable" fibre flow, in particular in the delivery section of the card. Up until now, this fact led to two unfavourable effects:
1. It is not possible to subject this unstable fibre flow to a regulating step, and PA1 2. the changes in the fibre flow over time can produce a sliver break, which necessitates a renewed threading up operation (with a subsequent transient phase).